I heard some of you develop web applications in c# (or think that's a good idea).
Since I like both c# and web a lot, I was wondering: what stack do you use, and how well does that work? Or is it just a pain in the not-to-be-named-rear-end?

There is only one stack: ASP.NET MVC Core.

The rest doesn't matter. Use whatever ORM, frontend, db, etc as you like. Only the choice for the ORM will be limited by the framework (I suggest Dapper).

I'll tag somebody that's very great at .net web @jase

How it works?

Well it's all new, with lots of changes every release, so documentation lags behind seriously. Questions and answers in online communities will conflict with each other and be almost always outdated. Bootstrapping will be a steep learning curve and awesome experience. Once you're set up, however, developing and extending is amazing. And it's good in performance and easy to read and understand.

I still went with Python and Flask though...

.NET Core is imho a really good stack. Specially going by their webapi template. Microservices in .NET take a little bit more setup than Flask, Slim etc. But the service is fast and really stable. All in all a very good choice of framework and their documentation is pretty good.

I am currently building a large demo with it and have been enjoying it thus far.

Thanks, guys!